1. Field of the Invention
The present invention relates generally to the construction of intravascular catheters. More particularly, the invention relates to intravascular catheters having guide wire receptacles which are compatible with rigid distal housings having ultrasonic imaging components therein.
Arteriosclerosis, also known as atherosclerosis, is a common human ailment arising from the deposition of fatty-like substances, referred to as atheroma or plaque, on the walls of blood vessels. Such deposits occur both in peripheral blood vessels that feed the limbs of the body and coronary blood vessels which feed the heart. When deposits accumulate in localized regions of a blood vessel, blood flow is restricted and the person's health is at serious risk.
Numerous approaches for reducing and removing such vascular deposits have been proposed, including balloon angioplasty where a balloon-tipped catheter is used to dilatate a region of atheroma, atherectomy where a blade or other cutting element is used to sever and remove the atheroma, and laser angioplasty where laser energy is used to ablate at least a portion of the atheroma. In addition to such therapeutic approaches, a variety of techniques for transluminal imaging of atheroma and other diseased regions of a blood vessel have been proposed, including endoscopic imaging techniques and ultrasonic imaging techniques. Common to all such techniques is the use of an intravascular catheter which is positioned at a desired location within the blood vessel to be treated or imaged.
Two alternative approaches may generally be employed to achieve such positioning. In the first approach, the vascular catheter is provided with a "fixed guide wire" secured to its distal end. The fixed guide wire is typically a coiled spring or other elongate resilient member having a preformed, curved tip. The catheter can then be guided through branches within the vascular network by rotating the entire catheter, causing the tip of the guide wire to enter a desired branch as the catheter is moved forward. In the second technique, an entirely separate "movable guide wire" is employed. The movable guide wire is itself a coiled spring or other resilient elongate member and will generally include a curved tip similar to that provided on the fixed guide wires described above. The vascular catheter being positioned includes a guide wire lumen which generally extends down the center of the entire length of the catheter and is sized to receive the movable guide wire. The movable guide wire is first positioned within the vascular system so that its distal end extends beyond the region of interest, and the intravascular catheter is then inserted over the movable guide wire using the guide wire lumen. Such procedures using movable guide wires are commonly referred to as "over-the-wire" insertional techniques.
The use of movable guide wires enjoys a number of advantages over the use of fixed guide wires. In particular, a movable guide wire allows positioning of relatively large diameter catheters which would be difficult to manipulate using a fixed guide wire. The presence of a movable guide wire also facilitates repositioning of the catheter during use and simplifies withdrawal of the catheter and replacement by either the same catheter or a different catheter.
The use of movable guide wires with certain types of intravascular catheters, however, is problematic. Many catheters have internal components within their distal end for imaging or interventional purposes, and such components can interfere with passage of the movable guide wire through the catheter. The use of movable guide wires has been particularly troublesome with imaging catheters of the type employing ultrasonic elements at their distal end, frequently in combination with rotating mirrors. It is undesirable to penetrate the ultrasonic element thus rendering passage of a movable guide wire through the center of the catheter undesirable. Thus, such catheters have normally employed fixed guide wires at their distal ends.
A second consideration in employing movable guide wires relates to their length. In many catheters, the movable guide wire is received in a lumen which extends the entire length of the catheter body. In order to both insert the catheter and remove the catheter while leaving the movable guide wire in place, it is necessary that the movable guide wire have a length equal to at least twice that of the catheter body. In this way, the proximal end of the guide wire may be held in place at all times while the catheter is being inserted or withdrawn. The use of such long guide wires, however, proved highly inconvenient, requiring manipulation of the guide wire in the catheter at great distances from the patient. To overcome these problems, "monorail" systems have been devised for certain types of catheters, including balloon-tipped catheters and laser hot tip catheters.
In such monorail designs, the guide wire lumen extends through only a very short wire lumen formed at the distal end of the catheter. Thus, the length of the guide wire can be reduced to a length which need only be equal to the length of the catheter plus the short length of the wire lumen at the distal end. Such monorail guide wire lumens, however, have not generally been employed in catheters having mechanical and electrical components in their distal end, such as ultrasonic imaging catheters where the passage of a guide wire, even for a short length, is problematic.
The use of such monorail designs with ultrasonic imaging catheters can be particularly problematic. Ultrasonic imaging catheters often require rigid housings, for example to hold the ultrasonic transducer in a fixed spatial relationship with a rotating mirror, and the presence of a rigid housing will frequently bind the passage of the guide wire. Such binding occurs particularly at the junctions between the rigid housing and the proximal and/or distal flexible regions of the catheters. Such flexible regions will often bend at rather sharp angles relative to the rigid housing, and such sharp bends can constrict a guide wire passing through a monorail-type lumen disposed on the side of the housing.
For these reasons, it would be desirable to provide ultrasonic imaging catheters having monorail-type guide wire lumens which are less prone to constricting the passage of a movable guide wire therethrough. In particular, it would be desirable to provide ultrasonic imaging catheters having rigid distal housings where the bending of the catheter is limited in the regions where a rigid housing joins a flexible proximal catheter body and a flexible distal tip of the catheter.
2. Description of the Background Art
U.S. Pat. No. 4,794,931, describes a vascular ultrasonic imaging catheter employing a rotating mirror and/or ultrasonic element to produce a two-dimensional image. The catheter is illustrated to include a fixed guide wire at its distal tip. U.S. Pat. No. 4,762,129, illustrates a balloon dilatation catheter having a laterally-offset lumen extending axially through the balloon and capable of receiving a movable guide wire. U.S. Pat. No. 4,748,982, discloses a balloon dilatation catheter having parallel lumens extending through the catheter body. A side port opens to one of said lumens proximally of the balloon, allowing a movable guide wire to extend from said side port the entire distance to the distal tip of the catheter. U.S. Pat. No. 4,821,731, describes an imaging catheter having a one-dimensional capability. The catheter is introduced over a radially-offset guide wire, but no provisions are made to reduce constriction of the guide wire. U.S. Pat. No. 4,402,684, describes a cannula having a soft tip. Trimedyne, Inc. of Tustin, Calif., sells a hot tip laser catheter having an enlarged metal tip with an axially-offset lumen for receiving a guide wire. The catheter is described in a brochure entitled "Announcing the Family of 2.5 mm Laserprobes" dated December 1987.